package com.yzzrjy.util;


public class UIDGeneratorUtils {

    private static long machineId = 0;

    private static long datacenterId = 0;


    private enum SnowFlakeSingleton{

        Singleton;

        private SnowFlake snowFlake;

        SnowFlakeSingleton(){
            snowFlake = new SnowFlake(datacenterId,machineId);
        }

        public SnowFlake getInstance(){
            return snowFlake;
        }
    }

    public static long getUID(){
        return SnowFlakeSingleton.Singleton.getInstance().nextId();
    }

}


class SnowFlake {

    /**

     * 起始的时间戳

     */

    private final static long START_TIME = 1674391084L;
    /**

     * 每一部分占用的位数

     */

    private final static long SEQUENCE_BIT = 6; //序列号占用的位数

    private final static long MACHINE_BIT = 0;  //机器标识占用的位数

    private final static long DATACENTER_BIT = 0;//数据中心占用的位数

    /**

     * 每一部分的最大值

     */

    private final static long MAX_DATACENTER_NUM = -1L ^ (-1L << DATACENTER_BIT);

    private final static long MAX_MACHINE_NUM = -1L ^ (-1L << MACHINE_BIT);

    private final static long MAX_SEQUENCE = -1L ^ (-1L << SEQUENCE_BIT);

    /**

     * 每一部分向左的位移

     */

    private final static long MACHINE_LEFT = SEQUENCE_BIT;

    private final static long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;

    private final static long TIME_LEFT = DATACENTER_LEFT + DATACENTER_BIT;

    private long datacenterId;  //数据中心

    private long machineId;    //机器标识

    private long sequence = 0L; //序列号

    private long lastTime = -1L;//上一次时间戳

    public SnowFlake(long datacenterId, long machineId) {
        if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0) {
            throw new IllegalArgumentException("datacenterId can't be greater than MAX_DATACENTER_NUM or less than 0");
        }
        if (machineId > MAX_MACHINE_NUM || machineId < 0) {
            throw new IllegalArgumentException("machineId can't be greater than MAX_MACHINE_NUM or less than 0");
        }
        this.datacenterId = datacenterId;
        this.machineId = machineId;
    }

    public synchronized long nextId() {
        long currTime = getNewTime();
        if (currTime < lastTime) {
            throw new RuntimeException("Clock moved backwards.  Refusing to generate id");
        }

        if (currTime == lastTime) {
            //相同毫秒内，序列号自增
            sequence = (sequence + 1) & MAX_SEQUENCE;
            //同一毫秒的序列数已经达到最大
            if (sequence == 0L) {
                throw new RuntimeException("too much uid in 1 second");
            }
        } else {
            //不同毫秒内，序列号置为0
            sequence = 0L;
        }

        lastTime = currTime;

        return (currTime - START_TIME) << TIME_LEFT //时间戳部分
                | datacenterId << DATACENTER_LEFT      //数据中心部分
                | machineId << MACHINE_LEFT            //机器标识部分
                | sequence;                            //序列号部分
    }

    private long getNewTime() {
        return System.currentTimeMillis() / 1000;
    }

}